1. Field of the Invention
The present invention concerns an amplifier circuit, of the type wherein the amplifier circuit has a transistor element with an input terminal, an output terminal and a third terminal, wherein an input signal to be amplified is supplied to the input terminal, and wherein the amplified input signal is emitted as an output signal at the output terminal.
2. Description of the Prior Art
Amplifier circuits of the above type are generally known. In such amplifier circuits the input terminal is normally connected with the output terminal via an ohmic resistor. The third terminal is connected with a zero potential via an additional ohmic resistor. For example, such an amplifier circuit is known from the prospectus from August 1990, “RF & Microwave Signal Processing Components” by the Adams-Russell Corporation. In principle this amplifier already works quite well; but it exhibits poor noise properties, in particular for a relatively small amplification factor.
An amplifier circuit of the type described above is likewise known from DE 10 2005 038 442 A1 and the corresponding US 2007/0040612 A1. In this amplifier circuit, the input terminal is connected with the output terminal via a negative feedback transformer. A similar design is known from the reference book “Breitbandige Ferrit-Hochfrequenztransformatoren—Schaltungen und Systeme” [“Broadband Ferrite High-Frequency Transformers—Circuits and Systems”] by Joachim von Parpart, Hohig Verlag, Heidelberg, 1997; see Page 125 there, for example. These amplifier circuits do in fact exhibit advantageous noise properties, but they require optimally securely coupled transformers as directional couplers, which is why ferrite must be used in the directional couplers thereof. Therefore they cannot be used in environments in which strong magnetic fields predominate.
Additional amplifier circuits of the type described above are known from U.S. Pat. Nos. 5,164,682 and 4,156,173.
An amplifier circuit of the type cited above is also known from U.S. Pat. No. 5,805,023. In this amplifier circuit the input terminal is connected with the output terminal via a first reactance. The third terminal is connected via a second reactance with a zero potential. One of the reactances is fashioned as an inductor, the other of the reactances as a capacitor.